Securities (Schedule of Contractual Maturities of Investment Securities Available for Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Abstract]
Due within one year, Amortized Cost	$ 111,449
Due after one year through five years, Amortized Cost	528,884
Due after five years through ten years, Amortized Cost	1,324,754
Due after ten years, Amortized Cost	1,061,728
Debt securities available-for-sale, amortized cost	3,026,815	$ 3,210,615
Due within one year, Fair Value	111,405
Due after one year through five years, Fair Value	526,821
Due after five years through ten years, Fair Value	1,341,174
Due after ten years, Fair Value	1,047,870
Debt securities available-for-sale, Fair Value	$ 3,027,270	$ 3,167,448